The present invention relates to a (meth)acrylic film having excellent elongation characteristics, in addition to high tensile strength. The film of the present invention can be used as a base material of an adhesive tape in interior and exterior materials for buildings, facing materials for fittings, and interior and exterior materials for vehicles because it has the above-mentioned characteristics. It is also useful as a substitute of a polyvinyl chloride resin which evolves a harmful gas during incineration because it is free from halogen.
As described above, a vinyl chloride resin having good balance between the tensile strength and elongation characteristics has hitherto been used as the facing film. However, there has recently been pointed out such a problem that deadly poison such as dioxin and a harmful gas such as hydrogen sometimes evolve during incineration. Thus it has been studied to replace by a resin free from chlorine.
An acrylic resin is employed to solve such a problem and, for example, a decorative sheet comprising a base film made of an acrylic resin and a protective layer made of an acrylic resin laminated on the surface of the base film and decorative sheet comprising a base film made of an olefinic resin and a protective layer made of an acrylic resin laminated on the surface of the base film are disclosed. See, for example, Japanese Unexamined Patent Publication (Kokai) No. 8-48014 and Japanese Unexamined Patent Publication (Kokai) No. 10-157018.
In case the acrylic resin is formed into a film, the resulting film is scarcely fit for use as a decorative sheet because it is rigid and brittle. To improve brittleness of the acrylic resin and to impart flexibility to the acrylic resin, a rubber component such as acrylic rubber particles is generally mixed and various techniques are proposed.
For example, there is disclosed an acrylic resin composition comprising (A) 20 to 98 parts by weight of a rigid thermoplastic acrylic resin obtained by polymerizing a monomer composed mainly of methyl methacrylate and (B) 2 to 80 parts by weight of polymer particles having a multi-layered structure, which is excellent in impact resistance (see, for example, Japanese Examined Patent Publication (Kokoku) No. 60-17406 and Japanese Examined Patent Publication (Kokoku) No. 60-30698). The polymer particles having a multi-layered structure has a three-layered structure comprising:
(I) a first layer formed of a rigid polymer obtained by emulsion polymerization of a monomer composed mainly of methyl methacrylate having Tg of 25° C. or higher,
(II) a second layer formed by polymerizing a monomer mixture comprising 45 to 99.99% by weight of an alkyl acrylate having C1-8 alkyl group, which has Tg of 25° C. or lower, 0.1 to 10% by weight of a polyfunctional grafting agent such as allyl (meth)acrylate, 5% by weight or less of a polyfunctional crosslinking agent such as dimethacrylate and 40% by weight or less of the other copolymerizable monomer, and
(III) a third layer formed by polymerizing a monomer composed mainly of methyl methacrylate having Tg of 25° C. or higher in the presence of the second layer, the polymer particles having a particle diameter of 200 to 900 Å, wherein the first layer accounts for 5 to 30% by weight of the multi-layer structure, the second layer accounts for 40 to 85% by weight of the multi-layer structure, and the third layer accounts for 10 to 30% by weight of the multi-layer structure.
However, these acrylic resins could not reconcile high tensile strength and elongation characteristics.
A resin obtained by adding an acrylic polymer having an amino group to an acrylic polymer having a carboxyl group (see Japanese Unexamined Patent Publication (Kokai) No. 10-310754). This reference discloses an adhesive composition obtained by adding (2) 1 to 40% by weight of a resin composition having Tg of 40° C. or higher and a weight-average molecular weight of 100,000 or less obtained by copolymerizing one or more kinds of monomers selected from alkyl methacrylate having 1 to 20 carbon atoms, cycloalkyl methacrylate, benzyl methacrylate and styrene as a main component with 0.5 to 10% by weight of an amino group-containing monomer to (1) 100 parts by weight of a resin composition having a weight-average molecular weight of 80,000 or more obtained by copolymerizing an alkyl (meth)acrylate having 1 to 12 carbon atoms as a main component with 0.5 to 10% by weight of a carboxyl group-containing monomer. However, this composition is an adhesive and is insufficient in tensile strength when used as a film.